USB flash drive is similar to a hard drive in that data is stored to its memory for retrieval by a computer's operating system. Removing a USB flash drive from a computer's USB port before it has been properly unmounted will corrupt the file structure, rendering the data unreadable. Repair the corrupted USB flash drive using software that comes with the Mac and Windows operating systems. The procedures for repairing the corruption, while dissimilar between operating systems, repair the file structure so that the USB flash drive can be used again.
Insert the USB flash drive into a USB port on the Mac. Double-click the Disk Utility program’s icon to launch it--the program is inside of the “Utilities” folder that is inside of the “Applications” folder.
Click the icon of the USB flash drive that is in the left column of the Disk Utility program’s main screen. Click the “First Aid” tab at the top of the program’s main screen.
Click the "Repair Disk” button below the “First Aid” tab. Wait as series of lines scroll down the centre of the window. Quit the Disk Utility program when the lines are no longer scrolling.
Drag the icon of the USB flash drive that can now be seen on the desktop to the Trash. Remove the USB flash drive from the USB port of the Mac.
Insert the USB flash drive into a USB port on a PC running the Windows 7 operating system. .
Right-click the icon of the USB flash drive that is on the desktop. Select "Properties”from the pop-up window that appears.
Click the “Tools” tab at the top of the new window that appears. Click the “Rebuild” button on the window.
Wait as a progress bar at the bottom of the window fills in from left to right. Close all the open windows on the desktop by clicking their red “X” buttons in the upper-right corner.
Right-click the icon of the USB flash drive that can now be seen on the desktop. Select “Eject” from the pop-up menu. Remove the USB flash drive from the USB port of the PC.